In U.S. Pat. Nos. 5,152,887, 5,158,649, 5,389,208, 5,441,605, 5,993,608, and 6,508,916 there are disclosed reclaiming processes for recovering process liquids such as, for example, recovering a processing liquid from a mixture comprising water, a processing liquid having a higher boiling point than water, optionally at least one additional component that is more volatile than the processing liquid and water, and at least one component that is less volatile than, and can be dissolved or suspended in the processing liquid.
In the processes disclosed in the aforementioned patents, the presence of undissolved salts (contaminates) complicates the process and makes it necessary to separate the salts in the process. With particularly reference to U.S. Pat. Nos. 5,993,608 and 6,508,916, both which are incorporated herein by reference for all purposes, there is disclosed a method wherein less volatile components, e.g., salts, which are either dissolved and/or suspended can be removed from the processing liquids under conditions that prevent any substantial degradation of the processing liquid. However, it would still be desirable if at least some of the salts could be removed prior to the processing liquid being subjected to the reclaiming process per se. Carbonate and bicarbonate salts dissolved in the processing liquids can build up during the reclaiming process leading to undesirable effects. It would clearly be desirable if these salts or other acid decomposable salts could be removed prior to the spent processing liquid entering the reclaiming system.
In one particular aspect of the processes described in the aforementioned patents, certain processing liquids such as alcohols, glycols, alkanolamines and other such materials can be used to prevent gas hydrate formation and/or remove acidic gases in oil and gas production, particularly on offshore platforms.
Hydrate control is critical to oil and gas production to prevent blockage of production tubing, valves and other equipment with clathrates. Hydrate inhibitors may include, but are not limited to, thermodynamic hydrate inhibitors such as alcohols (e.g. methanol) and glycols (e.g. monoethylene glycol), kinetic hydrate inhibitors (e.g. polyvinylcaprolactam, polymers, co-polymers or blends thereof) and anti-agglomerate hydrate inhibitors (e.g. N-butyl-N(3-(cocamino)-3-oxopropyl)butan-1-aminium acetate) are injected at or near the production manifold and flow back with the formation water, water of condensation and hydrocarbon phases being produced from the reservoir(s) of interest. In such a process, monoethylene glycol, for example, can become contaminated, with, but not limited to, water of condensation, formation water, salts contained in the formation water, flow assurance loop corrosion inhibitors, flow assurance loop corrosion products such as mill scale and iron sulphide. Certain contaminants/salts render the hydrate control ability of the selected hydrate inhibitor unusable for reinjection, thus requiring the contaminants to be removed prior to injection. The teachings in U.S. Pat. Nos. 5,993,608 and 6,508,916 provide methods and apparatus to carry out such contaminant removal from such a spent processing liquid.
In the case where the formation water contains salts of carbonates and/or bicarbonates and again with particular reference to oil and gas production and especially the prevention of gas hydrates, the carbonate and/or bicarbonate salts can range from relatively low levels in the spent processing liquid to concentrations beyond saturation levels, leading to the potential for formation of crystalline (precipitated) salts. During the processes disclosed in the aforementioned patents these salts are purposefully concentrated beyond saturation levels leading to the formation of crystalline (precipitated) salts. However, if these precipitated salts occur in spent processing liquid upstream of any solvent/reclaiming recovery process, be it regeneration where water is selectively removed, reclamation where salts are removed or a combination of thereof, the presence of these precipitated solids can lead to increased fouling of equipment and more complicated separation of the valuable processing liquid from these salts.
A further complication that acid soluble salts can induce is an uncontrolled increase in pH of the processing liquid over time. Testing has shown that bicarbonate can dissociate under temperature to carbonate and carbon dioxide. As the carbonate content of the process liquid increases, so does the pH. This may be beneficial for a period of time but if left unchecked extremely high pH values, in the neighbourhood of 12 can be achieved and for glycol based inhibitors it is possible to induce unwanted gelation. By removing the bicarbonates/carbonates, control on pH levels can be regained and maintained through selective addition